1. Technical Field
The present invention relates generally to an anti-jamming apparatus and method for a compact array antenna in a Global Navigation Satellite System (GNSS) anti-jamming system and, more particularly, to an anti-jamming apparatus and method for a compact array antenna, which can prevent a jamming signal and minimize the size of a GNSS signal invisible area while using fewer antenna elements than existing anti-jamming array antenna elements.
2. Description of the Related Art
A Global Navigation Satellite System (GNSS) is a global positioning system in which GNSS signals transmitted from a satellite are received on a ground, and the location, velocity, and time information of a receiver can be obtained. In order to receive GNSS signals and obtain location and time information, a receiver must receive GNSS signals from four or more satellites. For this, satellites that transmit GNSS signals are designed such that four or more satellites are simultaneously present in a visible area all over the world.
Meanwhile, since GNSS satellites transmit GNSS signals at a power of about 25 watts at an altitude of 20,000 km, the GNSS signals received on the ground are very weak. Due to this, GNSS signals are vulnerable to radio interference, and the reception of GNSS signals may be easily interfered with even by radio interference of low power.
Korean Patent No. 0866565 or the like discloses a scheme for spatially preventing a jamming signal using an array antenna as one of conventional technologies corresponding to GNSS jamming. In anti-jamming technology using an array antenna, jamming is prevented using a method of forming nulls in the direction of a jamming signal and forming beams in the direction of satellite signals via a beam-forming technique for adjusting the reception pattern of the array antenna.
If a weight of a complex number is applied to a signal, the magnitude and the phase of the signal may be changed. An array antenna beamformer for GNSS anti jamming controls beam patterns in such a way as to apply complex number-type weights to the signals of the array antenna, add the resulting signals, and form nulls and beams. In this case, a power minimization or power inversion technique is most widely used to calculate weights of respective antenna signals. This technique is advantageous in that preliminary information about the direction of GNSS satellite signals is not required so as to form beams.
Meanwhile, jamming signal prevention (anti-jamming) using the control of beam patterns causes a satellite-invisible area in which it is impossible for a receiver to receive satellite signals depending on the location of the GNSS satellite due to the shapes of nulls and beams that are generated. The satellite-invisible area is determined by beam patterns changed depending on the intensity and location of the jamming signal, and such a beam pattern is also changed by the structure of the array antenna and the number of antenna elements constituting the array antenna.
In a GNSS anti-jamming system using an array antenna, as the number of antenna elements increases, a beam (or a null) having a narrow beam (or null) width can be formed, and thus there is the advantage of securing a wide visible area.
Meanwhile, as the number of antenna elements increases, the dimension of a cross-covariance matrix that must be obtained to form a beam (or a null) is raised, so that an increase in power consumption required to operate a large number of elements, together with an increase in a computational load, are highlighted as disadvantages. Typically, it is known that an anti-jamming array antenna for military purposes has 6 to 7 antenna elements.
Therefore, in order to solve these disadvantages, an anti-jamming apparatus and method for a compact array antenna which can prevent a jamming signal using a small number of antenna elements and minimize the size of a GNSS signal invisible area are urgently required.